Vancouver Avian Research Centre

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Species: Wilson’s Warbler Wilsonia pusilla

Description:

Wilson’s Warbler is named after the ornithologist Alexander Wilson, who first described it in 1811, aptly titled as pusilla comes from the Latin term for ‘very small’. It is a common and widespread wood warbler found across Canada: the breeding range extends from Alaska to Newfound Land and partway down the western coast and Rocky Mountain region of the US. A neotropical migrant, it flies at night overland to its wintering home in Central America, going as far as western Panama; interestingly, it defends its winter territory with as much vigour as it does during the breeding season. This bird is also the only migrant warbler regularly found in the tropical high grasslands.

“Wilson” is also the mascot for the Vancouver Avian Research Centre’s workshops!

Identification: Wilson’s Warbler is a rather small songbird, about 10-12 cm in length and weighs around 8 grams. It has a long, thin tail and short, rounded wings, pinkish legs and feet and a small, dark-coloured bill.

Adult Male: The male is an unmarked and bright yellow underneath, darker olive-yellow on top, and has a distinguishing glossy, solid black cap (which extends across the crown with age). While his face is generally bright, the auriculars and nape are dark olive; wings and tail feathers are also dark, but edged with olive-yellow.

Adult Female: The mature female looks very similar to the adult male, but her cap is usually only partial, duller and mottled with olive, and her face may be a paler yellow than that of the mature male.

Juvenile: The juvenile male looks similar to the adult female, with flecks of yellow in his black crown, and is less bright overall than the adult male. Juvenile females have a mottled green-yellow crown, with relatively few black specks.

Similar Species: The Yellow Warbler is an overall bright yellow, and is distinguished by the reddish streaks down its breast and the absence of the black cap. The Orange-crowned Warbler is a much drabber yellow, with some faint streaking on its breast.

Behavior: Quite an active little bird, the Wilson’s Warbler frequently hops about, characteristically raising and flicking its tail. For feeding, it usually forages within 10 feet of the ground (but rarely on it), gleaning twigs and leaves for small insects and spiders (but includes berries in its diet as well). This bird also actively flycatches for its prey (note the rictal bristles at the base of its bill)!

Habitat: Generally preferring riparian habitat, this bird is usually found in willow and alder thickets near water, wet woodlands and shrubby fields, and often keeps low in the bushes. Its voice, a rapid and chattering chchchchchchch, a common song heard in the spring here in Vancouver, might give it away first!

Information:

Being a widespread species, Wilson’s Warblers will nest anywhere from sea level to alpine; they build a cup-shaped nest using ground vegetation such as moss, grass and leaves. Usually the nest is placed on the ground, hidden by a clump of grass, but Pacific coastal lowland birds tend to place their nests low in shrubs. The female builds the nest herself and she will incubate the eggs for an average of 12 days; the clutch typically consists of 3-6 cream-white eggs with reddish-brown spotting.

There are three subspecies of this bird that are currently recognized and W. p. chryseola is the one found in Vancouver and along the Pacific coast. An interesting note, western birds tend to have more yellow on the face than do their eastern cousins.

The longevity record for a wild Wilson’s Warbler is a male at 6.8 years!

Conservation Status:

It holds a status of Least Concern, but this is being kept under close watch, as there seems to be a downward trend - particularly in western populations, most likely due to large-scale habitat loss. It does, however, do quite well in shade-grown coffee plantations!
 
Capture Rates


Although caught in every month from April through October, capture rates (2010-2012; standardized as birds captured per 100 net hours) of Wilson's Warbler go through a large peak in May as they pass through Colony Farm to their nearby breeding areas. As long distance migrants, these warblers move south for the winter as seen by our zero capture rates between November and March.


 

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